Phase modulation transmitter



Nov. 12, 1963 c. J. WEIDKNECHT ETAL 3,110,863

PHASE MODULATION TRANSMITTER Filed Sept. 21, 1959 5 R O T m V m 6% fleaJI'Wa'dinecZ fi/arlej Ease/z, 3% WWW ATTORNEY5 United States Patent3,110,863 PHASE MQDULATIQN TRANSMITTER Charles J. Weidlmecht and CharlesRosen, lhiladelphia, Pa, assignors to Vector Manufacturing Company, acorporation of Pennsylvania Filed Sept. 21, 1959, Ser. No. 341,124 13(Claims. (Cl. 325l) This invention generally relates to improvements inR.-F. transmitters for producing a phase modulated carrier signal and isparticularly well adapted for use as a mobile telemetering transmitterfor aircraft and missiles were factors such as small size and weight, aswell as low power consumption are paramount consideration.

It is accordingly a principal object of the invention to provide a phasemodulated transmitter of miniature size, weight and low powerconsumption compatibly with providing the necessary stability, shockresistance and related characteristics necessary for such mobileapplications.

A further object is to provide such a transmitter employing completelysolid state elements.

A still further object is to provide an R.-F. phase modulatedtransmitter employing a unique configuration of transistor circuitssupplying wide range phase modulation coupled with improyed stabilityand insensitivity to variations in temperature or voltage supplyvariation.

Other objects and additional advantages will be more readily understoodby those skilled in the art after a detailed consideration of thefollowing specification taken with the accompanying drawings wherein:

FIG. 1 is an electrical schematic drawing illustrating an R.-F.transmitter according to the present invention; and

FIG. 2 is an electrical schematic drawing showing fur" ther details ofthe coupling circuit of FIG. 1 for impedance matching the final poweramplifying stage.

Referring now to the drawing for a detailed consideration of onepreferred embodiment according to the present invention, there is showna high frequency transmitter system including an oscillator circuitstage generally designated Ill, a separate modulator circuit stage ll, aplurality of frequency multiplier stages 12, 13, 14, and 15, and a poweramplifier stage to, all being connected in cascaded relationship toproduce a phase modulated carrier signal over the secondary winding ofan output transformer 17 leading to an antenna or other load (notshown).

Although not limited to such application, the present invention isparticularly well suited for use as a telemetering transmitter operatingin the frequency range between 215 and 260 megacycles and producing awide range phase modulated carrier. To obtain this wide rangemodulation, the oscillator stage iii is adapted to operate at aconsiderably lower sub-harmonic frequency than the desired carrierfrequency, and this sub-harmonic frequency is then phase modulated bymeans of modulator stage 11. The resulting phase modulated signal isthen multiplied in frequency by a plurality of stages l2, 13, 14, and 15until the desired high frequency is obtained thereby to alsoproportionally increase the amount of phase modulation. All of thestages are constructed of components of minimum size, weight and powerconsuming capacity and preferably all employ transistors, as shown.

Referring specifically to the oscillator stage 16', a preferredembodiment comprises a three element transistor 18 having its emitterelement being energized by a positive source of potential over groundline 19 and its collector element energized by an equal valued negativesource of potential on line 26 through first and second series connectedresistors 21 and 22. To provide the "ice necessary feed back forsustaining oscillations at constant frequency, a crystal Z3interconnects the base element with the collector element to establish astable resonant frequency and a coupling capacitor 24 furtherinterconnects the base element with the emitter element to complete thefeedback loop. For biasing the base element at its proper position alongthe transistor characteristic curves, the base element is also connectedto the central junction of a potential divider circuit comprised ofseries connected resistors 25 and 2,6 having opposite ends thereof beingenergized from the positive and negative sources of potential, as shown.

Since the frequency of the oscillator stage it may be varied by changesin the D.-C. energizing potential, a reversely poled or Zener diode 27,paralleled by a filter capacitor 28, is connected from line 2? leadingto the negative potential supply, to ground line 19 leading to thepositive supply, thereby to stabilize the 'voltage potential energizingthe various elements of the transistor 18 and prevent changes in thevoltage sources from exerting any measurable effect on the frequency ofthe oscillator.

The constant frequency sub-harmonic carrier signal being generated bythe oscillator stage 10' is taken from the collector element oftransistor 18 and thence directed through a coupling capacitor 3t) andresistor 31 to the emitter element of the separate modulator transistor32. According to the present invention, this separate modulator stage isprovided to supply three functions. Primarily, the modulator stageprovides wide range phase modulation of the sub-harmonic carrier signalas is believed evident. However, the separate modulator stage is alsoeffectively decoupled from the oscillator thereby to sub stantiallyprevent loading of the oscillator despite a varying modulating signaland thus enable the oscillator to continuously function at constantfrequency as desired despite Wide range modulation and slow or rapidchanges in the modulating signal.

In addition to these functions, there has heretofore existed the problemof preventing (independent oscillations in transistor modulators due tothe fact that the interelement capacitance existing between base andemitter elements and base and collector elements is sufliciently largeto normally provide feedback therebetween and sustain oscillation at thehigh frequencies involved. Ac cording to the present invention, however,this problem is eliminated by the unique configuration of the combinedoscillator and modulator stages. More specifically, the base element ofmodulator transistor 32 is preferably grounded with respect toalternating currents through the positive source of potential 19, thecarrier signal is introduced at the emitter element, and the modulatedcarrier is taken from the collector element. With this configuration,therefore, the smaller interelement capacitance (large reactance)between the collector element and base, and the emitter element and basecannot sustain oscillations, whereas the larger interelernentcapacitance (smaller reactance) between the emitter and collector isutilized in obtaining the phase modulation. Consequently, the groundedbase configuration of the modulator stage taken with the groundedemitter configuration of the oscillator stage provides the desired widerange modulated carrier without variably loading the oscillator orintroducing undesired independent oscillations therein.

Returning to the modulator stage, the collector element of transistor 32is energized from the negative source over line Zlland through aresistor 33 and tuned circuit generally designated 34, and the baseelement thereof is self biased by means of a parallel connected resistor35 and capacitor 36 to alternating current ground line 19, which asdiscussed above is energized by a positive D.-C. source. In common withthe oscillator stage It the D.-C. potential feeding the modulatortransistor 32 is stabilized and made constant by connecting a Zenerdiode 37 and para Ming capacitor 38 intermediate the positive D.-C.energized ground line 19 and the junction between resistor 33 andresonant circuit 34.

in operation, a modulating signal is introduced over line 39 and throughcoupling capacitor it} to the base element of transistor 32 therebyvarying the electrical conduction between the emitter and collectorelements. However, since the D.-C. potential is applied from thecollector to the base elements, the equivalent circuit shows that thismodulating signal serves to vary the phase of the voltage existingacross the collector to base elements due to the values of theinterelement capacitance existing between the emitter to collector andthe collector to base taken with the fact that the transisor is operaingin the meigacycle frequency range. The net result is that thesub-harmonic oscillator signal appearing across the resonant circuit 3 2is phase shifted by an amount proportional to the modulating signal overline 39 whereby the circuits and ll function as a phase modulatedoscillator having a wide range of phase shift.

To increase this sub-harmonic frequency to the much higher frequencydesired and at the same time to proportionally increase the phase shiftrange, the resonant circuit 34 is tuned to a higher harmonic of theoscillator signal whereby the voltage appearing across the tuned circuit34 is a higher harmonic multiple of the modulator signal but reduced inamplitude. The tuned circuit 34 is preferably formed of a high Qtransformer whose primary winding is in parallel with a capacitor, asshown, with the circuit being tuned by a suitable core slug 41 or thelike. The secondary winding 42 of the transformer energizes the emitterelement of a grounded base amplifying transistor 43.

Transistor 43 serves to amplify the lower order harmonic signal and isalso provided with an output resonant circuit E4 comprised of coupledtransformers and parallel connected capacitors tuned by slugs 45 and 46to a higher harmonic frequency than the input tuned circuit 34. Thustransistor 43 provides a first frequency multiplication stage'ser vingto increase the phase modulated carrier by a harmonic multiple of theoscillator frequency.

in a similar manner, stages 13, 14, and are preferably identicalfrequency multiplying stages in cascaded array and including transistors47, 48, and 49, each being provided with tuned transformer tank circuitsat the input and output thereof and with each tuned circuit beingprogressively adjusted to produce a higher harmonic multiple frequencythan the last thereby to progressively increase the frequency inharmonic multiples of that desired.

It is to be particularly noted that each of the tuned frequencymultiplier stages 12, 13, 14, and 15 are arranged with the base elementsof the transistors bein'g grounded to A.-C. and en rgized with apositive D.-C. potential and with the input circuits being connected tothe emitter element and the output circuit to the collector element. Thesource of D.-C. energizing potential is applied across the collector tobase elements in each stage. By this circuit configuration, optimumadvantage is taken of the intereleme-nt capacitance at the highfrequency involved in achieving maximum gain and frequency response.

It is also to be particularly noted that a common positive and negativesource of potential is employed to energize and bias all stages of thetransmitter and that all stages, with the exception of the oscillatorstage 10, are of the grounded ibase variety. The reason for this uniquecon-figuration is to obtain optimum stability despite minor variation inthe energizing and biasing sources. More specifically, it is known thatthe reactive components or interelement capacities of the transistorsvary with change in the biasing potentials. Accordingly, this effect isminimized by using a common voltage source for all emitter and collectorelements.

To obtain the necessary power amplification of the phase modulatedcarrier signal, the final stage 16 of the transmitter is preferablyformed of a pair of differentially connected power amplifyingtransistors 5i} and 51. The base elements of transistors 50 and 51 arecommonly con nected together and to the A.-C. ground line 19, and theinput signal is differentially passed from the emitter elements of eachtransistor to the collector elements thereof.

Considering the input to the power amplifying stage 16, the phasemodulated carrier is taken from the secondary o=f tuned transformer 52and differentially directed through capacitors 53 and 54 to the emitterelements of transistons 5t} and 51. The collector elements of eachtransistor 50' and 51 are connected to opposite terminals of the primarywinding of output transformer 17 whose center tap 70 receives negativeD.-C. potential over line 20 and through a choke coil 71 which serves toprevent the A.-C. carrier from entering the D.-C. source. Consequently,the phase modulated signal differentially passes from the emitter tocollector elements of each transistor and is applied in push-pull acrossthe output transformer 17 and thence coupled to the load (not shown).

The output transformer 17 is, of course, tuned to the' desired frequencyby means of parallel connected lined and variable capacitors 55 and 56,respectively, and the emitter elements of both transistors in the inputcircuit are supplied with a positive bias potential by being D.-C.-coupled to the positive source of potential on line 19 through a biasresistor 5'7 and choke coils 58 and 59, as shown, the choice coils 58and 59 preventing the A.-C.- carrier from being grounded through line19.

It is to be particularly noted that the final frequency multiplier stage15 is impedance matched to the power amplifier stage 16 by a two sectionimpedance matching network. This two stage network is obtained byemploying the interelement capacities existing between the emitter andbase elements of the power transistors 50 and 51 as best illustrated inFIG. 2. Referring to FIG. 2 for an understanding of this two stageimpedance match ing circuit, there is shown the tuned transformer 52leading from the collector element of frequency multiplier stage 15 andthe remaining reactive and resistive elements intermediate this stageand the power amplifying stage 16. As shown, the phase modulated carriersignal appear-s across the secondary winding 69 of transformer 52 andthence is differentially directed through capacitors 53 and 54, asdescribed above, to pass over lines 61 and 62 to the emitter elements oftransistors 50 and 51, respectively. However, at the high frequenciesinvolved, the interele ment capacity 63 existing between the emitter andbase elements of transistor 50* provides a significant reactance in thecircuit as shown between lines 61 and A.-C. ground, as does the similarcapacitance 64 of transistor 51. Consequently, the coupling capacitance53 forms with the interelement capacitance 63 of transistor 50 a firstpotential divider circuit for line 61 and the coupling capacitance 54forms with the interelement capacitance 64 out transistor 51 a secondpotential divider circuit for line 62 with a net result that thetransformer 52 and capacitor potential dividers, as shown, provide a twostage impedance matching network coupling the final frequencymultiplying stage 15 with the power amplifying stage, as desired.

We claim:

1. in a high frequency phase modulated transmitter of improvedstability, a crystal controlled transistor oscillator including atransistor having emitter, collector, and base elements, and a crystalinterconnecting the base and collector elements, resistance meansproviding a D.-C. bias on the base element and means applying a D.-C.potential across the emitter and collector elements, a grounded basetransistor phase modulator comprising a transistor having base,collector and emitter elements, means coupling the collector element ofthe oscillator transistor to the emitter element of th modulatortransistor, and means introducing a modulating signal intermediate theground connection and the base element of the modulator transistor, aplurality of transistor fre quency multiplication stages and tunedcircuit coupling means interconnecting said modulator and said frequencymultiplier stages in cascaded relation.

2. in the transmitter of claim 1, a differential power amplificationstage including a pair of transistors in back-to-back relation, eachhaving emitter, collector, and base elements with the base elementsthereof commonly connected to ground, and tuned resonant circuit meansdifferentially coupling the last of said cascaded frequency multiplierstage to the emitter elements of said power amplifier transistors.

3. In the transmitter of claim 2, a capacitor in series circuit relationwith the emitter element of each of said differentially connectedtransistors in the power stage thereby providing in conjunction with theinternal capacitance of the transistor a potential divider to impedancematch said last frequency multiplying stage with said power amplifyingstage.

4. In a phase modulated transmitter operating in the megacycle frequencyrange, a crystal controlled transistor oscillator, a grounded base phasemodulator comprising a transistor having a grounded base element andconnected to receive the carrier signal from said oscillator at itsemitter element and produce a phase modulated carrier signal from itscollector element upon receiving a modulating signal intermediate itsbase element and ground, and means for multiplying the frequency of thephase modulated carrier thereby to increase rnany fold the oscillatorfrequency and proportionally increase the phase modulation, theinterelectrode capacity between the emitter and collector elements beingsufficiently large at the frequency of the oscillator to transmit aphase I isplaced signal therethrough in the magnitude range of themodulated signal from emitter to collector electrodes whereby the signalat the collector electrode is phase displaced from the oscillator signalin proportion to the modulating signal.

5. In the transmitter of claim 4, said multiplying means including atransistor having base, emitter, and collector elements with the baseelement being grounded and the emitter and collector elements each beingcoupled to resonant circuits tuned to different frequencies in the ratioof frequency multiplication desired.

6. In a phase modulated transmitter, a crystal controlled transistoroscillator having base, emitter, and collector elements with the emitterelement thereof grounded with respect to A.-C. currents and with thecrystal interconnecting the base and collector elements, means phasemodulating said oscillator comprising a second transistor having base,collector and emitter elements with the base element thereof connectedto receive a modulating signal for substantially controlling theetlective resistance between emitter and collector elements, meanscoupling the emitter element of the modulating transistor to thecollector element of said oscillator, and a tuned frequency circuit inthe output of the modulating transistor to increase the frequency andphase modulation proportionally to a harmonic of the oscillatorfrequency, the interelectrode capacity between the emitter and collectorelements being large at the frequency of the oscillator to provide aconstant phase displaced signal component therethrough in the range ofmagnitude of the varying signal component from the emitter to collectorelectrodes.

7. In the device of claim 6, means stabilizing the potential energizingsaid oscillator and modulator transistors, said means including a Zenerdiode in circuit with the collector elements of each transistor.

8. In a phase modulated transmitter having great stability, a crystalcontrolled transistor oscillator having a grounded emitter element, acrystal interconnecting the base and collector elements and la Zenerdiode in circuit with the collector to stabilize the D.-C. potentialapplied thereto, a phase modulator transistor having emitter, collectorand base elements with the base being connected to a ground throughcircuit means introducing a modulating signal, means coupling theemitter of the modulator transistor to said oscillator, and a tunedresonant circuit connected as an output load in circuit with thecollector element of the modulator.

9. In the transmitter of claim 8, a plurality of frequency multiplierstages responsive to the output of the modulator for progressivelyincreasing the oscillator frequency by harmonics thereof.

10. In the transmitter of claim 9, each frequency multiplier stageincluding a transistor having base, emitter, and collector elements,with the base element grounded with respect to A.-C. signals and theemitter element connected to receive the transmitter signal.

11. In a transmitter for megacycle frequency transmission, a stabilizedoscillator producing a high frequency signal, a phase modulatorcomprising a transistor having base, emitter and collector electrodes,means connecting the emitter and collector electrodes of the modulatorin series with the oscillator signal, and means introducing a modulatingsignal to the base electrode, the interelectrode capacity from theemitter electrode to the collector electrode being large at theoscillator frequency to provide a shunt path through the transistor thatis constantly phase displaced from the resistive signal componentpassing from the emitter electrode to the collector electrode and havinga constant amplitude in the range of amplitude of the resistive signalcomponent, whereby the vector sum of the two components at the collectorelectrode is phase displaced from the oscillator signal in proportion tothe modulating signal.

12. A transistor phase modulator comprising a transistor having a baseelectrode, emitter electrode, and collector electrode, means introducingan oscillating signal to the emitter elect-rode, means coupling a loadcircuit to the collector electrode, and means introducing a variableamplitude modulating signal to the base electrode, said transistorhaving a large interelectrode capacity between the emitter collectorelectrodes at the frequency of the oscillating signal to transmit aconstant amplitude signal component from the oscillating signal to theload circuit therethrough, 'and said transistor producing a variableamplitude signal component from the emitter electrode to the collectorelectrode and to the load proportional in amplitude to the modulatingsignal and in an out-ofphase relationship with the interelectrodecapacity signal component, whereby the vector sum of the two signalcomponents at the load is varied in phase from the oscillating signal inproportion to the amplitude of the modulating signal.

13. In a high frequency transmitter having an oscillator, modulator, andpower amplifier, a high frequency coupling circuit for impedancematching a signal to the power amplifier, said power amplifier includinga transistor having base, emitter, and collector electrodes, with thesignal being coupled from the emitter electrode to the collectorelectrode and being controlled by energizing the base electrode, saidhigh frequency coupling circuit comprising a capacitor in series withthe emitter and collector electrodes and providing in conjunction withthe interelectrode capacity from the emitter to base electrodes apotential divider to impedance match the signal to the power amplifier.

References Cited in the file of this patent UNITED STATES PATENTS2,298,930 Decino Oct. 13, 1942 2,587,294 Dorbec Feb. 26, 1952 2,589,542De France et a1. Mar. 18, 1952 2,606,284 Van Weel Aug. 5, 1952 2,682,639Haner June 29, 1954 (Other references on following page) Friend Feb. 15,Shockley Aug. 2, Van Overbeek Nov. 5, Van Overbeek July 15, KircherSept. 23, Lin Oct. 21, Goodrich Jan. 20, Hruska May 19, Herring May 26,Aronson June 23, Harrison et a1 May 3,

teggerda May 10, 1960 Kircher et a1. Feb. 14, 1961 OTHER REFERENCESJeffe et -a1.: Frequency and Fhase Modulation, Proc. I.R.E., vol. 33,N0. 3, March 1945, pp. 200, 201.

Lo et a1: Transistor Electronics, September 26, 1955, pages 225-240.

Article: A Trensistorized 150 M.C.F.M. Receiver, pages 693-699 ofProceedings of the IRE for April 1958.

Circuit for Space Probes, Bennett et -a1., Electronics, June 19, 1959,pages 55-57 relied on.

1. IN A HIGH FREQUENCY PHASE MODULATED TRANSMITTER OF IMPROVEDSTABILITY, A CRYSTAL CONTROLLED TRANSISTOR OSCILLATOR INCLUDING ATRANSISTOR HAVING EMITTER, COLLECTOR, AND BASE ELEMENTS, AND A CRYSTALINTERCONNECTING THE BASE AND COLLECTOR ELEMENTS, RESISTANCE MEANSPROVIDING A D.-C. BIAS ON THE BASE ELEMENT AND MEANS APPLYING A D.-C.POTENTIAL ACROSS THE EMITTER AND COLLECTOR ELEMENTS, A GROUNDED BASETRANSISTOR PHASE MODULATOR COMPRISING A TRANSISTOR HAVING BASE,COLLECTOR AND EMITTER ELEMENTS, MEANS COUPLING THE COLLECTOR ELEMENT OFTHE OSCILLATOR TRANSISTOR TO THE EMITTER ELEMENT OF THE MODULATORTRANSISTOR, AND MEANS INTRODUCING A MODULATING SIGNAL INTERMEDIATE THEGROUND CONNECTION AND THE BASE ELEMENT OF THE MODULATOR TRANSISTOR, APLURALITY OF TRANSISTOR FREQUENCY MULTIPLICATION STAGES AND TUNEDCIRCUIT COUPLING MEANS INTERCONNECTING SAID MODULATOR AND SAID FREQUENCYMULTIPLIER STAGES IN CASCADED RELATION.